What it means
The inverter phase U of drive motor A reports junction temperature above the protection threshold. Sustained high phase current.
At a glance
- Usually lights the check-engine light
- The engine or gearbox may go into limp mode
How it works
Drive motor A's inverter phase U switches current through one of the motor's three phase paths. The control module monitors the phase U junction temperature and sets this code when it exceeds the protection limit, often after sustained phase overload or loss of local cooling.
Common causes
Most likely first.
- Sustained phase overload
- Local cooling failure
Symptoms
- EV/hybrid system warning light on
- Reduced motor power or torque
- Possible limp mode or vehicle shutdown
How to diagnose it
- Read freeze-frame data and related codes to see the phase U temperature, motor load and operating conditions when the fault set.
- Check live inverter temperature and phase data, if available, to see whether phase U remains hotter than phases V and W.
- With the vehicle powered down as directed by the manufacturer, inspect the inverter cooling system for leaks, blocked flow or damaged connections.
- Check for conditions that could overload phase U, including related motor phase or wiring faults recorded by the control module.
- Test the inverter cooling and phase U circuit using the manufacturer's diagnostic procedure to distinguish a cooling fault from an electrical overload.
Common fixes
- Restore coolant flow by correcting a blockage or leak in the inverter cooling circuit.
- Repair damaged phase U wiring or connections if tests identify a fault.
- Correct the confirmed motor or load condition causing sustained phase U overload.
- Repair or replace the inverter if testing confirms an internal phase U thermal fault.
Can I keep driving?
Avoid heavy acceleration, towing or sustained high load, and stop if the vehicle limits power or warns of overheating. Continued operation can trigger limp mode or shutdown.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.